1. Field of the Invention
The present invention relates to image encoding and decoding, and more particularly, to apparatuses and methods for encoding and decoding a binary image having a pixel value of two kinds or less, or a text image including a boundary portion.
2. Description of Related Art
Multimedia apparatuses such as mobile phones and personal digital assistants (PDAs) having a video graphic array (VGA) resolution of 640×480 or 480×460 read image data in units of lines, generate one-dimensional (1-D) blocks having a predetermined number of pixels for each line, and perform coding in units of 1-D blocks to generate a bitstream. The 1-D block may consist of 8×1 pixels or 4×1 pixels. However, when an original image as illustrated in FIG. 1A is coded in units of 1-D blocks, the image quality of a binary image 111 or a text image 113 including a boundary as illustrated in FIG. 1B may be seriously reduced. Also, when an original image having a definite boundary portion 131 as illustrated in FIG. 1C is coded with a fixed compression ratio, bits to be assigned are short for a lower portion 133 of one frame, which not only reduces image quality but also reduces an encoding efficiency, so that a desired compression ratio is not achieved.